The simulated magneto-optical force, which in the presence of a longitudinal static magnetic field is exerted on atoms resonant with the high-intensity light field of two counterpropagating, linearly polarized laser beams with an angle of ∼45° between their directions of polarization, is described in the dressed-atom picture. This allows an easy calculation of the force on atoms at rest, illustratively explains its nonzero wavelength average, and provides an intuitive understanding of its dependence on the atomic velocity. For a simple atomic model transition (J=0⇆J’=1) the velocity-dependent force is calculated by considering the motion along the dressed states and using the Landau-Zener model for the nonadiabatic transitions at the avoided level crossings. It is shown that for a certain relation between Larmor and optical Rabi frequency a perfectly diabatic motion takes place, leading to a disappearance of the velocity-tuned (doppleron) resonance structure.

We study the ionization of atomic hydrogen by a high-frequency circularly polarized field. We solve numerically the time-dependent Schrödinger equation for the atomic wave function, which beforehand is expanded in a Coulomb-Sturmian basis. We analyze the ionization from various initial states differing by their azimuthal quantum number m, the principal and the angular quantum numbers being equal to 2 and 1, respectively. At high field intensities we observe important differences in the ionization yield: strong stabilization is observed for m=0 and m=1 while for m=-1 the atom is almost completely ionized. We also study the electron energy spectra for the same cases and show that they are characterized by a multiple splitting of the above-threshold-ionization (ATI) peaks. The behavior of the ionization yield as well as the structure observed in the ATI spectra are explained in terms of the ac-Stark shift and width of the atomic levels. We also consider some of the aspects of the underlying dynamics by means of a very simple essential-state model.

This paper treats the problem of locking a molecular bond at a length other than the equilibrium distance, with the help of optical electric fields. Locking conditions for single-color fields are examined, and slowly decaying locked wave functions are sought. These wave functions are then used as target functions in an optimal control procedure. The resultant solution is an optimal field that creates a wave function as close as possible to the target function, followed by the application of a locking single-color field that can keep a large part of this wave function at the given position. An objective of the approach is to eventually extend the optimal control theory to the preparation of molecules in quasistationary nonequilibrium states for further study by spectroscopic or other means. Results are reported for a model of CsI with two potential-energy surfaces, one with a repulsive character.

The decay of coherence when a quantum system interacts with a much larger environment is usually described by a master equation for the system reduced density matrix and emphasizes the evolution of an entire ensemble. We consider two methods that have been developed recently to simulate the evolution of single realizations. Quantum-state diffusion involves both diffusion, where the individual quantum trajectory fluctuates through a Wiener process deriving from the environment, and localization to a coherent state, an eigenstate of the relevant Lindblad operator describing the coupling of the system to the environment. We demonstrate the localization process for different initial states and utilize the Wigner function to depict this localization in phase space. We concentrate on quantum states that can be expressed as a superposition of appropriate coherent states. For an initial superposition of two coherent states (a Schrödinger ‘‘cat’’), one of the two components will dominate the evolution. For initial Fock states, which can be described as a continuous superposition of coherent states on a ring, localization takes place when one coherent state is selected from that ring where each component has nearly the same energy as the original Fock state. We also consider the localization from a nonclassical squeezed ground state, which can be expressed as a superposition of coherent states along a line in phase space. The second simulation method considered is the state vector Monte Carlo, or ‘‘quantum jump,’’ approach, which relates to the direct counting of decay quanta. In the case of an initial Schrödinger ‘‘cat,’’ we find that when no quantum is detected the ‘‘cat’’ shrinks, but when a quantum is detected, the Schrödinger ‘‘cat’’ ‘‘jumps’’ from one type of ‘‘cat’’ to another with different internal phase. For an initial squeezed state we show how quantum jumps lead to individual realizations which are superpositions of two squeezed states.

A single light beam, generated by type-II down-conversion, is split by a beam splitter. When a set of quartz plates is inserted into the single beam, the coincidence counting rate between the split beams exhibits a 100% frequency-beating modulation. This nonclassical phenomena is a manifestation of a two-photon entangled state in which the two-particle state is entangled simultaneously in spin and space-time.

The coexistence of several attractors in the coherent collapsed state of a laser diode with optical feedback is investigated. These attractors are unstable tori that bifurcate from different external cavity modes. As the feedback rate is increased, these tori undergo different types of quasiperiodic routes, such as frequency locking, period doubling, or the appearance of a third incommensurate frequency. In the fully developed coherent collapsed state, the tori are all unstable, and the phenomenon of intermittence appears. Lyapunov exponent calculations demonstrate that this state presents hyperchaotic and high-dimensional dynamics. These results are explained qualitatively in terms of the multiattractor behavior found.

The intensity of a second-harmonic light beam generated in potassium dihydrogen phosphate (KDP) crystals immersed in the optically dense fluid 1-bromonaphthalene has been observed as a function of the incident angle of the fundamental beam of a mode-locked neodymium glass laser. The laser pulses have polarization in the [11¯0] direction with respect to the KDP crystallographic axes. The phase-matchable second-harmonic generation at total reflection and in the vicinity of the critical angle were performed. The existence of a nonlinear Brewster angle has been demonstrated and its utilization may include using a null method for a precise measurement of the relative magnitude of nonlinear optical susceptibility components of materials. The results agree well with the theory of Bloembergen and Pershan [Phys. Rev. 128, 606 (1962)].

The spatial structure of a gain-guided amplifier is naturally described by a set of nonorthogonal modes. We present an analysis of the mode structure of an amplifier with a focused Gaussian gain. It is found that the modes are spatially narrower and have a different radius of curvature than the corresponding free-space modes. A calculation of the signal-to-noise ratio shows that the spatial structure of the input field has a significant effect on the amplifier noise performance.

The occurrence of steady-state squeezing in a coherently driven three-level atom of the Λ configuration is found to be highly sensitive to the detection process of the fluorescence field. We show that there is no steady-state squeezing when the two atomic transitions equally contribute to the detected fluorescence field. There is no squeezing even when only one of the two possible transitions contributes to the detected fluorescence field, if the decay rate of the contributing transition is smaller than or equal to the decay rate of the other transition. Squeezing may occur only when the decay rate of the transition that exclusively contributes to the detected fluorescence field is larger than the decay rate of the other transition. Moreover, when the squeezing attains its maximum value, pure two-level squeezing is involved. The system reduces to a two-level system in which both the basic three-level dynamics and the two-photon coherences are destroyed.

We demonstrate the possibility of quenching the effects of noisy lasers by intense coherent fields. For this purpose, we study the spectrum of resonance fluorescence from two-level atoms irradiated by bichromatic fields, where one field is coherent and the other stochastic. The spectrum is seen to be very sensitive to the frequencies of the two fields. In particular, we find a dramatic narrowing of the Rabi sidebands in the spectrum when the fluctuating field is tuned to the frequency of the Rabi sideband in the spectrum. We interpret the results in a dressed-state representation, revealing that the atom is sensitive to the fluctuating field, only when that field can induce resonant transitions between the dressed levels. Our calculation of the decay rates of the dressed levels predicts a narrowing of the sidebands by a factor of 4, when the driving field is broadband, while at the same time the central peak in the spectrum is broadened. Surprisingly, we find that there is the possibility of observing very narrow resonances even when noisy lasers interact with the atom.

We describe the generalization of the Jaynes-Cummings model to a system with non-Abelian U(2) gauge symmetry and find its exact solutions in the holomorphic representation involving both bosonic and fermionic variables. The model admits a representation of a four-level atom as a system consisting of a given number of N=1,2,3,4 fermions linearly coupled to a bimodal quantized radiation field. The non-Abelian gauge symmetry specifies the linear coupling of the radiation field modes to the fermion fields. This is essential in order to obtain a fully integrable system of interacting bosons and fermions.

The alternative multimode theories of parametric down-conversion based on either nonlinear susceptibility models or the general quantum electrodynamic interaction are critically examined and shown not to be equivalent. The predictions can be qualitatively different; in contrast to the former, within the framework of the latter, it is necessary to define more than one type of nonlinear susceptibility in order to describe one-photon and two-photon count rates.

We study cooperative effects on the radiation interaction of a pair of two-level atoms with a spatial separation r≪${\lambda }_0$ much closer than the optical wavelength of the dipole transition. In this regime we allow for charge exchange between the atoms (hybridization), which leads to qualitatively different behavior in contrast to an isolated pair of atoms because of the presence of the monopole Coulomb interaction. The interaction of the atoms with the radiation field and an external classical driving field is treated within a master equation approach. The numerical as well as the analytical results indicate the existence of quantum beats in the radiative decay of the system. In the case of an external driving field the system shows a dark resonance for a fixed detuning independent of the strength of the external field.

Dynamical restrictions to the squeezing achievable by means of a degenerate optical parametric oscillator (OPO) are considered by quantum-statistical diagram techniques. We determine optimal pumping conditions which maximize the degree of squeezing in the output signal of the OPO. The maximal spectral squeezing in the OPO’s output radiation is found to scale as ${\mathit{N}}_2^{\mathrm{-}2/3}$ where ${\mathit{N}}_2$ is the number of photons in the pump mode.

We develop a many-body quantum Monte Carlo wave-function approach to analyze the dissipative interaction of ultracold free atoms with the radiation field reservoir. A Markovian master equation for the identical atoms that neglects the dipole-dipole interaction is derived within the framework of quantum field theory. The effective Hamiltonian obtained by a decomposition of the master equation explicitly depends on the quantum statistics.

Light emitted from laser-driven atoms often has squeezed quadrature fluctuations reflecting the phase dependence of the atomic source excited into a coherent superposition by the driving field. In this paper, we study the maximum squeezing in the emitted light fields from three-level atoms, paying particular attention to the role of atomic coherences in governing the optimum squeezing which is possible. Some phase dependent nonlinear optical processes have the potential for substantial quantum noise reduction at useful intensities: for example, four-wave mixing involving atomic systems has already been used to generate quadrature-squeezed light. The threoretical description of such a source is generally complicated with damping processes, coherent and incoherent pumping, and so on, all needing to be taken into account. Fully quantum treatments are available, but the basic physics of the process is often difficult to grasp in the necessarily complicated analysis. Although less important from the point of view of efficient practical sources of squeezed light, studying the generation of squeezed light in simpler systems such as two- or three-level atoms interacting with one or two modes (as in Jaynes-Cummings models) or in spontaneous emission or resonance fluorescence gives greater insight into the fundamentals of the squeezing process. In particular, the relationship between the atomic coherences and the degree of squeezing in the generated fields can be explored. We study the maximum (optimized) squeezing that can be obtained in the emitted fields from the irreversible decay from three-level atoms for any choice of initial conditions, excitations and decay process, for all quadrature components and for all possible configurations (V, Λ, and ‘‘ladder’’ systems).

We show that for V and Λ systems, optimum squeezing is actually associated with a two-level state (in a suitable basis) involving a single one-photon coherence, but for ladder systems the state for maximum noise reduction is not equivalent to a two-level system and involves a single two-photon coherence and no intermediate state population. We pay particular attention to whether the total field is in a minimum uncertainty state, and the nature of the atomic state associated with maximum squeezing, especially whether it is a mixed or pure state. In the case where the initial free field has a zero amplitude at the detector and the source atoms are confined to a region small compared to the wavelength (Dicke source) we show that the squeezing in the total field is given in terms of the squeezing in the source field, and hence related to atomic populations and atomic one-photon and two-photon coherences for the case of three level atom. Previously unconsidered source-free field interferences terms are shown to be zero. The choice of quadrature phase and frequency is optimized to minimize the source field normally ordered variance. We then minimize further with respect to the choice of atomic density matrix elements subject to the constraints that the density matrix is Hermitean, positive, and has a trace equal to unity. In all cases we find that the optimum squeezing is produced when the source field is in a minimum uncertainty state.

Quantum-optical master equations—exemplified by the Jaynes-Cummings model with damping—are turned into numerical partial differential equations of first order for phase-space functions, which are generalizations of the Wigner function and its relatives. The time dependence of these phase-space functions originates solely in the atom-photon interaction; all other time dependences, in particular the dissipative contribution of the photon damping, are accounted for by the time-dependent operator bases to which the phase-space functions refer. The judicious choice of operator basis also effects the absence of second-order derivatives in the partial differential equation. Our first-order equations are hyperbolic and can be integrated conveniently along their characteristics. As an illustrative application we study how the Jaynes-Cummings revivals are affected by photon damping. We show how to handle squeezed reservoirs and how to apply the method to laser cooling.

We present a theoretical analysis of coherent atomic motion through a straight atomic waveguide constructed from a hollow optical fiber. Atoms are guided by the evanescent light field at the fiber’s interior glass-vacuum interface. The atoms’ internal structure is modeled by a ${\mathit{J}}_{\mathit{g}}$=0 to ${\mathit{J}}_{\mathit{e}}$=1 transition. The atomic wave functions are determined and the loss rates due to spontaneous emission, tunneling to the wall, and nonadiabatic transitions are estimated. The influence of Casimir-Polder forces is considered. We conclude with a discussion of the feasibility of the proposed waveguides.

The temporal evolutions of the electron distribution function and the electric field in a dense, hot, multiply charged plasma due to the presence of a sharp temperature gradient from one side (plasma–cold matter contact) and a sharp density gradient from the other side (plasma-vacuum boundary) are studied. The prospects for x-ray lasing in such a plasma are discussed. The analogy with a p-n junction semiconductor laser is emphasized.

A scalar Green’s-function technique is used to derive coupled-amplitude equations for electromagnetic waves propagating in a three-dimensional structure with a radially varying refractive index. The vector nature of the problem is discussed and a method is outlined for reducing the vector wave equations to characteristic scalar equations. These scalar equations are then solved via an exact coupled-amplitude formalism, and closed-form solutions are compared with numerical results for the particular case of a spherical Bragg region. The derivation of the coupled-amplitude equations for vector spherical waves is a significant portion of the calculation, described in the companion paper [Sullivan and Hall, following paper, Phys. Rev. A 50, 2708 (1994)], of the radiative effects due to the presence of a spherical Bragg structure. Furthermore, the formulation is a powerful complement to previously developed Debye potential and transfer-matrix methods.